BACILLUS COLI COMMUNIS. 447 



sesses also a considerable reducing power, converting 

 nitrates into nitrites, as may be demonstrated by the 

 addition of sulphuric acid in the proper proportion to 

 a bouillon or peptone culture, when a pink coloration 

 results. 



On Potato. On potato the growth is rapid and 

 abundant, appearing after twenty-four to thirty-six 

 hours in the incubator as a yellowish-brown to dark 

 cream-colored deposit covering the greater part of the 

 surface. But there are considerable variations from 

 the typical growth on potato; there may be no growth 

 at all, or it may be scanty and of a white color. These 

 variations are due at times to the bacillus, but more 

 often to variations in the potato. 



Gas-production. The bacillus coli grows rapidly 

 in media containing glycerin and sugar, particularly 

 glucose, causing active fermentation with liberation of 

 carbonic acid and hydrogen gas. Cultivated in solid 

 media, to which glucose has been added, the gas-pro- 

 duction is recognized by the appearance of numerous 

 bubbles along and about the points of growth ; in fluid 

 media it may be demonstrated in the fermentation- tube. 

 Grown on lactose-litmus-agar, the colonies are pink 

 and the color of the surrounding medium is changed 

 from blue to red, showing the production of acid. 



Milk is coagulated by the growth of the bacillus 

 coli after twenty-four to seventy-three hours in the in- 

 cubator, with the production of gas and acid; very 

 rarely acid may be produced and no coagulation occur. 

 The coagulation of the milk is hastened by warming. 



The thermal death-point of the colon bacillus from 

 feces was found by Weisser to be 60 C., the time of 

 exposure being ten minutes. When the bacilli from 



